Gray balance and dot expansion principle (two)
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Third, the expansion of outlets and the expansion curve of outlets
(1) Expansion of outlets
Dot enlargement is a dot size change that occurs during the plate making and printing process, which results in an actual dot area larger than the desired dot area.
(2) Expanding types of outlets
The process of occurrence by dot enlargement can be divided into two categories, which are dot enlargement in the plate making process and dot enlargement in the printing process.
1. Expansion of outlets in the plate making stage
The expansion of the dot produced during the plate making process mainly exists in the two processes of film output and printing. The main factor affecting the expansion of the dot when the film is output is the optical nonlinear effect of the photo-aligning machine, which can be solved by the calibration of the alignment machine. For the linearization of the photo-distribution machine; the factors affecting the expansion of the netting process in the printing process are more, and can only be compensated by the method of controlling the process parameters. This kind of dot enlargement is not reflected when setting the color separation parameters. When setting the color separation parameters, it is necessary to consider the dot gain generated during the printing process.
2. The dot enlargement of the printing process
The expansion of outlets is an inevitable phenomenon in the printing process, and its impact on the quality of printed matter is crucial. Under the action of printing pressure, the ink will expand to the periphery of the dot. At the same time, due to the compression deformation of the lining, the relative slip between the printing plate and the paper (or printing plate and blanket), the rubber market and the paper will also cause the dot to expand. Obviously, the expansion of outlets due to expansion and slippage is always unavoidable.
In addition, the double reflection of the paper on the light can also cause the dot to expand. About 80% of the white light is reflected when white light hits the white paper, but only 10% of the white light is reflected when the white light hits the intersection of the dot covering the ink and the white paper. In this way, the human eye adds a circle of ink around the real dot while viewing the dot. Although the outlets did not actually change, the information that was felt was that the outlets expanded.
(3) Expansion of outlets of different output devices
The development of computer peripheral technology has led to the diversification of output devices, and also allows for a variety of options for image output. Different types of output devices have different dot expansion laws, and even the same device may generate different dot gains. For example, black-and-white laser printers have a much larger dot gain than offset presses, where the dot gain is typically around 35%, and the inkjet printer's dot gain is lower.
Therefore, the control of dot gain is not only meaningful for printing on a press, it is also important for output to a printer. Although general printers are not PostScript printers, they do not recognize separation settings parameters, but trying to control their dot gain is important for accurate image output.
Dot extension control for non-Post Script laser printers or other printers cannot be achieved with color separation settings, but can be adjusted with certain color adjustment commands, such as using the Brightness/Contrast command to brighten the image so that the printed image Not to look very dark.
(4) The intermediate adjustment point expansion value of different ink paper combinations
Each ink paper combination in the Ink Colors list has a specific set of intermediate adjustment dot expansion parameters. This set of parameters is an estimate of the interpolated dot gain of each color version of the different ink paper combinations. The company's actual experience with each type of ink paper combination. For users without expertise, these parameters not only serve as a guide, but in most cases good color separation results are obtained.
For the convenience of the reader, Table 4-4-1 lists the estimated midtone dot gains for all ink-paper combinations in Photoshop.
Table 4-4-1 Different ink paper combination color version intermediate adjustment dot expansion default value
Numbering Ink and paper combination name
Estimated value of interpolated network points for each color version/%
Green version Yellow version Magenta version Black version
1 AD-LITUO (Newsprint) 33 30 30 30
2 Dainippon Ink 12 8 8 8
3 Eurostandard(Coated) 13 9 9 9
4 Eurostandard(Newsprint) 33 30 30 30
5 Eurostandard (Uncoated) 19 15 15 15
6 SWOP (Coated) 24 20 20 20
7 SWOP (Newsprint) 33 30 30 30
8 SWOP (Uncoated) 29 25 25 25
9 Toyo Inks (Coated Web Offset) 16 12 12 12
10 Toyo Inks(Coated) 12 8 8 8
11 Toyo Inks (Dull Coated) 12 8 8 8
12 Toyo Inks (Uncoated) 19 15 15 15
From the tabular data, the following rules can be summarized:
1 All ink and newsprint combinations use the same dot gain value, and the dot gain value is the largest;
2 Among the four color versions, the green dot has the largest dot gain value, and the other three color plates have the same dot gain value;
3 In the newspaper printing, the difference between the dot value of the green version and the expansion value of the other color version is 3%, and the difference between the other versions of the ink paper combination and the other three outer color versions is 4%;
4 Coated paper (coated paper) has a smaller dot gain than offset paper.
(5) Standard network expansion curve
Photoshop has a default set of dot gain values for the ink and paper combinations listed in the Ink Colors list. Each ink paper combination has an estimate of the midtone dot gain for each color version. The software uses this value to create colors. The version of the dot expands the curve and adjusts the dot size of the entire image. Such dot gain curves are called standard dot gain curves and are provided by software.